Here’s the problem: Apple doesn’t hold the keys to the shooter’s iPhone. The only way to break through an iPhone’s encryption lock is with a passcode, which isn’t stored on Apple’s servers.

The FBI could try to guess the shooter’s passcode, but if investigators guessed wrong 10 times, the shooter’s iPhone would permanently erase all of the content stored inside.

So the judge said Apple had to provide “reasonable technical assistance” to help it unlock the phone, including developing a software tool that would let investigators guess a passcode as many times as it needed to in order to break into the phone.

In a public letter opposing the FBI’s demands, Tim Cook didn’t mince words.

“The government is asking Apple to hack our own users and undermine decades of security advancements that protect our customers,” Cook said. “The same engineers who built strong encryption into the iPhone to protect our users would, ironically, be ordered to weaken those protections and make our users less safe.”